This invention is concerned with heat resistant and dimensionally stable expandable plastic particles and the molded articles produced from the expandable plastic particles. Expandable styrene particles and molded articles produced therefrom have been known. The particles are produced by making styrene monomer into a granular polymerizate by suspension polymerization followed by impregnating the granules with a readily volatile blowing agent.
For the production of foamed molded articles, there is a known method wherein expandable styrene particles containing a readily volatile blowing agent are prefoamed by heating with steam followed by heat-molding with steam in a mold which can be closed, but not closed too tightly. However, because the monomer constituting the polymer is styrene, the foamed molded article cannot be used either as heat insulation material for pipes used at relatively high temperature, or in any other field where heat resistance is required.